1. Technical Field
The present invention is directed to sundials, and more particularly toward a sundial for accurately and conveniently displaying time during the summer and winter months and for indicating the date.
2. Background Art
Sundials are devices that show the time by the sun producing a shadow on a marked surface. Sundials have been known for thousands of years, with one of the earliest examples being a horizontal bar of about one foot in length with a T-shaped structure at one end that existed in Egypt about 1500 BC. The length of the shadow cast by the T-shaped structure on the horizontal bar gave the time. Also known for hundreds of years are sundials with a horizontal projection surface and vertical gnomon for producing a shadow on the horizontal projection surface as the sun moves across the sky. One significant problem with such structures is that as the sun moves from east to west in the sky, the shadow moves at different rates along the horizontal projection surface, requiring uneven spacing of the indicia of time. In a more advanced version of such a sundial, the planar tracing surface is made parallel to the equatorial plane so that the shadow advances at a constant rate, allowing the markings on the planar projection surface to be constantly spaced, which improves the ease of telling time. The gnomon on such a structure is placed at the latitude angle with respect to a local horizontal plane.
Even this more advanced version of the sundial has serious shortcomings. Most notably, the sundial typically displays the time in a manner that is convenient to read during the summer months. In the winter months, with the sun dipping below the equatorial plane, the display of time is less convenient to observe. In addition, these conventional sundial structures do not provide indication of the date.
The present invention is directed to overcoming one or more of these deficiencies.